Phenol-formaldehyde adhesives



paper, plywood, or other materials.

Patented Sept. 12, 1944.

Wendell S. Niederhauser, Moorestown, N. J., and Matthew W. Miller, Philadelphia, Pa., assignors to The Resinous Products. & Chemical Company, Philadelphia, Pa., a corporation of Delaware No Drawing.

v '5 Claims. This invention relates to phenol-formaldehyde condensates which contain one methyl sulfonate group for three to to eight phenyl nuclei, which are soluble in water and hydroxylated organicsolvents, which provide aqueous "solutions that are relatively stable within the pH range of 1 to 10.5, and which are converted'to insoluble.res-

ins when heated. The inventionalso concerns the process by which said resins'are obtained.

The condensates of this invention are particularly suitable for use as adhesives resistant to boiling water, for binding wood veneer, paper, cork, abrasives, etc.

Water-soluble phenol-formaldehyde condensates in the so-called B stage which have heretofore been available have been stable in-aqueous tions. In the presence of the required alkali, the curing of such phenol-formaldehyde condensates has required relatively high temperatures. This is a definite disadvantage in the fields in which water-soluble phenol-formalde= hyde condensates may be used, such as the use ofthese condensates as adhesives or binders for In bonding materials containing moisture, there are often difficulties arising from use of elevated temperatues in curing in that steam pockets may be formed within the article-being bonded,- with consequent disruption.- p

The objects of this invention are to provide a water-soluble condensate fromphenol and form- Ap'plication August1'4, 1941, Serial No. 406,808 a solutions only, under definitely alkaline condipreferably carried out with the reactants in aqueous-solution. After the initial condensation, the

products are brought to an advanced resinous state without separation of, insoluble resinous materials by heating an aqueous solution of the sulfonated condensate until the viscosity of a solution having a 50% solids content is at least G on the Gardner-Holdt scale and the solution becomes dilutible with water in all proportions. The solution may be.'left in an alkaline state, but it is preferred that prior to use it be rendered acid; If desired, the resinous condensate mayv be converted to a solid by spray or drum drying. The dry product may be stored for long periods of time and may be mixed with a powderedacid so that acidic solutions ready for use as adhesives may b prepared directly from the dry mixture.

In acidifying either the powder or solution, any dilute mineral acid or an organic acid may be used to lower the pH. Strong, concentrated acids are apt to cause gelation or precipitation and are preferably avoided. Suitable acids include phosphoric, succinic, maleic, oxalic, acetic, etc. Maleic acid may be introduced by way of its anhydride, which is, particularly suitable for mixing with the dried condensate. It is often advantageous to use an ammonium salt in con- Junction with one of the acids, as, for example, ammonium oxalate in conJunction with oxalic :a'cid. The'strength and amount of acid added aldehyde which is suitable for use as an adhesiye,

to provide aphenol-formaldehyde type condensate which-yields stable aqueous solutions within a range cfpI-I between 1 and 10.5, and to provide such a condensate which may be cured in the presence of .an acid catalyst at low temperatures to form a' water-proof, insoluble resin."

By "water-proof" it is understood that the glue bond willnot be destroyed by water at temperatures up to and including the boiling point when tested in a standard, test strip of 3-plyfi," plywood as detailed P 13 1;. I

'It is now found that a water-soluble condensate in U. S. Navy Specifications 39 meeting all of the above requirements is prepared by condensing phenol or metacresol and formaldehyde under alkaline conditions'to form a water-soluble methylol' phenol, and reacting said methylol phenol with a sulfite to form 'one u-sulfonicgroup, or methyl :sulfonate group, for

three to eight phenyl nuclei. These steps of condensing and reacting may be carried out consecutively or "simultaneously.- These steps are l :to'sthe solution of condensate determine its useful life, but no'diiliculty is encountered in preparing acidic solutions of condensates which are stable over the working periods required for preparing and applying them as adhesives, which are rapidly cured at moderate and favorable tem.

peratures to give strong water-resistant bonds.

As an alkaline catalyst-in promoting the initial reaction of formaldehyde and phenol, there may be used any basic substance such as sodium or potassium hydroxide, a quaternary ammonium hydroxide -examples of which are benzyl trimethyl ammonium hydroxide, dibenzyl ,dimethyl ammonium hydroxide, and the likesodium carbonate,. lime, sodium sulflte, etc. i

The soluble inorganicsuliites are particularlydesirable as they help to supply a needed component without necessitating the addition of excess inorganic materials. It is generally desirable to use the minimum amount of any given alkaline catalyst which will promote the initial condensation. A pH between 8 and 11 is preferred in the initial stages.

Formaldehyde is most conveniently used in the form of the usual commercial aqueous solution. It may also be used in the form of a polymer and in part may be supplied by other methylenic tion and polymerization has been reached. The most satisfactory adhesives are obtained when the viscosity of the solution (adjusted to 50% solids) reaches Ci or-higher on the Gardner-Holdt scale.

- but also in such hydroxylated solvents as the monaldehyde is not utilized inthe final product, 9.1-

though a ratio as high as 1.7 may be used.

While phenol itself is of primary importance.

since it gives condensates which have a-considerable degree of solubility in water, there may be 'used in place of phenol substituted phenols, such as metacresol, which likewise give water-soluble methylol phenols. Also, other substituted phenols which have ortho and/or para positions available for substitution and are capable of acquiring methylol groups by reaction with formaldehyde (so-called methylol-formingphenols") be' used in conjunction with phenol, metacresol; or the like.

and a substituted phenol provides adhesives with The use of mixtures of phenol special properties. As typical of such substituted phenols. there may be mentioned the dihydroxydiphenyl suliones, the alkyl phenols, such as tertbutyl phenol, acyl phenolaalkoxy phenols, the polyhydroxyp'olyphenyl alkanes or cycloalkanes, such as dihydroxyphenyl dimethyl' methane, dihydroxydiphenyl, catechol, resorcinol, phloro-.

hols, of mixtures of alcohols and water.

ohydric alcohols, including methanol, ethanol, v

isopropanol, etc., in glycols and glycol others, including ethylene glycol, diethylene glycol, triethylene glycol, etc., and other polyhydric alco- .hols, including glycerine, or in mixtures of alco- When non-volatile alcohols are used, and the condensates cured, a softening or plasticizing action is obtained. This is particularly valuable in rendering the bond more flexible, as in binding cork,

in making laminations with fabric, or in impregnating cloth, wood, or paper.

Although the condensates may be cured in an alkaline condition, it is'preferred that they be Y .cured in an acid condition, since lower curing temperatures may thenbeused. The range of curing temperatures .is exceptionally wide, however, so that. the condensate of this invention may be used in conjunction with other resinous compositions glucinol, etc. The amount of such phenol which may be added to phenol itself or other phenols giving a water-soluble methylol phenol is determined by the solubility inwater of the resulting co-condensate. In all cases, it is desirableto maintain solubility in aqueous solutions without the addition of any considerable amount of an organic solvent and blending agent, such as methanol or ethanol, which maybe used if required. a v I when the phenol and formaldehyde have been reacted in the presence of an alkaline catalyst to form a primary addition product, this primary product, or meth'ylol phenol, is reacted with an inorganic sulflte to form methyl sulionate groups within the defined ratios. The term sulflte is here used to include both normal sulfltes, such as sodium or potassium sulflte, and acid suliltes, such as NaHSOa, NHKHSOa-etc.v The acid suliltes are to be preferred since they introduce a smaller amount of inorganic material and produce a condensate which may be carried to an acid pH with the minimum addition of an acidifyin; agent. In effecting the initial to 1011 0. maybe used. .As the reaction is exothermic, it is desirable to control the reaction by regulation of temperature and/or rate of addition of the reactants. In general, reaction temperatures'between about 55 C. and 80 C. give a sumciently rapid rate oi reaction, with excellent concondensation in the presence of an alkaline catalyst, temperatures up which cure at 110 C. or higher. By proper adjustment -of catalyst, curing may be effected even at room temperatures. j

Further details of the preparationof the partially u-sulfonated phenol-formaldehyde 'condensates useful as adhesives are shown in the following examples.

' Example 1 A mixture of 100 parts by weight of phenol, 86.5

parts of 37% aqueous formaldehyde, and 134- "parts of sodiumsulflte was prepared and slowlyheated to -55? C. Therei then occurred an exothermic reaction after which the reaction mixture was maintained at 50-55 C. for two hours and then at 80-85' C. for two hours. The

temperature was then dropped to 50 C. and 300 parts of phenol slowly added, followed by 397 parts of 37% aqueous formaldehyde. The temperature rose to 70 C. and was maintained at this point until..the viscosity .of the solution.

. reached H on the Gardner-,Holdt viscosity scale.

The'reaction mixture was then cooled to room temperature and brought to a pH Just above 7 by addition of 18% hydrochloric. acid. There was then added 244 parts'of water and the reaction mixture heated at 80-90 C. until a viscosity between S and W was reached. The temperature was then dropped to 75-80 C. and held at thispoint until a Gardner-Heidi; viscosity between Z and Z:' was obtained. The resultin solution remained stable over a considerable period of time.

trol thereof, so that insoluble products do not form. .After the initial condensation, it is still desirable to control the reaction which ensues when a sulflte is added, as, again. the reactioniis exothermic. In} preferred procedure, the reaction mixture. from the primary condensation is brought to about -70 C. and the required amount of sulflte added. The temperature is r then maintained below 100 C. (about 80 C. being preferred) until an advanced degree of condensa- It was acidified with a little lactic acid and applied as a glue between layers of cardboard, which were pressed at 115 C. to form astiifboai'd.

Example 2 4 Tea cool solution of 10.6 parts'of sodium hydroxide in 21.3 parts of water there were addedparts of phenol and '121 parts of 31% aqueous formaldehyde solution. The mixture .was

warmed to about 50 C. when an exothermic reaction ensued.- The reacting solution was held at 55 C. byexternal cooling and, alter the initial reaction had subsided, at 50-55 C. for five hours. The solution was then cooled and brought to a pH between 7.5 and 8 with dilute hydrochloric acid. 27.4 parts of sodium ibisulilte. was then These condensates are soluble not only in water I hyde added.

parts of sodium bisulfite, 5.37 parts of sodium sulfite, and 126 parts of 37% aqueous formaldehyde. The mixturewas heated until an exothermic reaction set in and then cooled externally to control the reaction. The reaction mixture was-then heated at 9095 C. until the viscosity was if to W. At this point, 53.1 parts of water was added and heating continued, to bring the viscosity to ZZ3. This product was likewise useful as an adhesive. v

v Example 4 was then added 100 parts of phenol and temperature raised to 80 C. for three hours. 23.4

parts of sodium bisulfite was added and heating I continued until a viscosity of U on the Gardner- Holdt scale was reached. The resin solution was diluted with 56 parts of water and heating continued at 80 C. until a viscosity of Z was reached.

This product was acidified with a little dilute hydrochloricacid and applied to veneers which were pressed together and heated at 120 C. to

I give a strong, water-proof bond.

Example 8 A mixture of 100 parts of phenol, 3.1:; parts of sodium sulflte, and 120 parts of 37% aqueous formaldehyde was heated until an exothermic reaction began and then held-at 80 C. for three hours. C., 13.1 parts of sodium bisulfite added. and the temperature held at 80 C. until a viscosity of W was reached. At this point, 56parts' of water was added and the solution held at 75 C.-until a vis-- A mixture of 100 parts of phenol, 5.37 parts. of

sodium sulflte, and'lzoparts of 37% aqueous formaldehyde was heated until an exothermic reaction ensued, thereupon maintained below 85 C.- by external cooling until the reaction subsided, and heated at about 80 C. for three hours. At this point, 17.7 parts of sodium bisulfite was added and the reaction therewith controlled by cooling. The mixture was then heated to 90 C. and carried to a viscosity of GL. 53.1 parts of water was then added and condensation continued to a viscosity between Z and Z3. The solution was spray-dried to a powder, which was kept some months without changing. Mixed with powdered oxalic acid, it was dissolved in water to form an acid-stable adhesive which was readily cured to an insoluble state at 110 C. to 120 C.

' Example 5 cosity of Z was-obtained. It will be noted that in this preparation the ratio of phenol to formaldelute acids. It may be dried at a moderate or low temperature to give a solid which remains soluble and reactive.

Example 9 A mixture of 100 parts of phenol, 16.75 parts or sodium-sulflte, 27.6 parts of sodium bisulfite, and

I 73.5 parts of water was warmed to C. and

thereto was slowly added 128 parts of 7% aqueous formaldehyde. The reaction mixture was xmaintained at 90-95 C. until a viscosity of 0 was reached, whereupon the temperature was kept at about 80 C. until the viscosity became Z4. In

. this preparation, the ratio of phenol to formaldea viscosity between T and W was reached. The

solution was then cooled, brought to a pH above 7 but under 7.5 with sulfuric acid, and further condensed with heat to a viscosity between X and Z.

Example 6 A mixture of 100 parts of a commercial cresol (containing 40-45% of metacresol, 27% of paracresol, 25% of xylenols, and 2-3% or orthocresol) 12.85 parts of 37% aqueous formaldehyde. and. 20.3 parts of sodium sulfite was heated for four hours at 95-100 C. The reaction mixture was cooled and.92.5 parts of aqueous 37% formaldes The solution was then held at 70-75 C. until a. viscosity between Z and Z: was obtained. This solution may be acidified, applied as an adhesive, and hardened with heat to give strong, water-proof bonds.

Example 7 g A mixture of 12.8 parts of dihydroxyphenyl di-' methyl methane, 1.49 parts of sodium hydroxide; and 131 parts of-37% aqueous formaldehyde'solution was heated at C. for one hour. There hyde available for resin formation was 1 to 1.1

and the sulfite to phenol ratio was 0.37 to 1. The solution was stable to acid. When applied as an adhesive, it was cured at relatively lowtem- 'perature to give astrong, water-proof bond.

Example 10 A mixture of 100 parts of phenol, 152 parts of 37% aqueous formaldehyde, and 4.45 parts of sodium sulfite was heated at 80-90 C. for two and a half hours. 18.5 parts of sodium bisulflte was then added and the condensation continued at 80 to 90 C. until a viscosity of Zin the Card-- ner-Holdt scale was reached. At this point, 49 parts of water was added and the reaction again carried on until the viscosity reached Z3. In this preparation, the total ratio of formaldehyde to phenol was 1.7 to 1, but the ratio in the final product was-1.5 to 1. The ratio'of sulfite to Phenol was 0.2 to 1.

We claim:

1. A process for preparing a water-soluble resinous composition which is stable -in cold aqueous solutions having a pH above 1.5 and under 10.5, which comprises condensing only three components, namely,.-.-('a) a phenol from (b) formaldehyde, and (c) a water-soluble inorganic sulflte, said phenol and'said formaldehyde being condensed below C., in the ratio of one mol of said phenol to 1.1- to 1.5 'mols of said formaldehyde and in the presence of an alkaline catalyst, .to; form a water-soluble The reaction mixturewas cooled to 70 methylol phenol, said methylol phenol then being reacted with said water-soluble inorganic sulflte in the ratio of one mol of said sulilte to 3 to 8 mols of saidmethylol phenol, thereby to form sulfonate groups in the resulting con- "den-sate, and thereafter heating the sulfonatedcondensate of said three components in aqueous solution until the viscosity of a. 50% aqueous solution thereof becomes at least G on the Gardner-Holdt scale.

2. As a new product, a water-soluble, partially polymerized, thermosetting phenol-formaldehyde composition which contains methylene sulfonate groups, .which.dissolves in water to give solutions which may be acidified without precipimethylol phenol then being reacted 'wlth said water-soluble inorganic sulflte in the ratio ofone mol of said sulflte to 3 to 8 mols of said methylol phenol, thereby to form methylene sulfonate groups in the resulting condensate, and thereafter heating the sulfonated condensate of said three components in aqueous solution until the viscosity of a 50% aqueous solution thereof becomes at least G on the Gardner-Holdt scale.

3. As a new composition of matter, suitable as a waterproof adhesive when dissolved-in water.

a water-soluble dry .powder comprl sing a mixture of a solid acid and a dry, water-soluble, partially polymerized, phenol-formaldehyde condensate containing methylene sulfonate groups,

said condensate being the product'obtained by condensing only three components, namely, (a) a phenol from thegroup consisting of phenol and metacresol, (b) formaldehyde, and (c) a water-soluble inorganic sulflte, said phenol and .said formaldehyde being condensed below 100 0., in the ratio of one mol'of'said phenol to 1.1

to 1.5 mols of said formaldehyde and in the pres-V 'ence of an alkaline catalyst. to form a watersoluble methylol phenol, said methylol phenol then being reacted with "said water-soluble insolution until the viscosity of a 50% aqueous solutionof-said sulfonated condensate becomes at least G on the Gardner-Holdt scale, and

-. thereafter drying said condensate.

4. A plywood adhwive giving waterproof bonds comprising an. aqueous solution of a water-soluble, partially polymerized, phenol-formaldehyde condensate which may be dissolved in water'and acidified without, substantial precipitation of insoluble resin and which is the product obtained by condensing only three components, namely,

' (a) a phenol from the group consisting of phenol and metacresol, (1)) formaldehyde, and (c) a in the ratio of'one mol of said phenol to 1.1 to

water-soluble inorganic sulflte, said .phenol and said formaldehyde being condensed below 100 C., in' the ratio of one mol of said phenol to 1.1 to 1.5 mols of said formaldehyde and in the presence of an alkaline catalyst, to form a watersoluble methylol phenol, said methylol phenol then being reacted with said water-soluble inorganic sulflte in the ratio of one mol of said sulflte to 3, to 8 mols of said methylol phenol, thereby to form sulfonate groups in the resulting condensate, and heating the sulfonated con- .demate of said three. components in aqueous 1 solution until the viscosity of a aqueous solution of said sulfonated condensate becomes at least G on the Gardner-Holdt scale.

5 A plywood adhesive giving waterproof bonds comprising an acidified aqueous solution of pH above 1.0- of a water-soluble, partially polymerized, phenol-formaldehyde condensate which maybe dissolved in water and acidified without substantial precipitationof insoluble resin and which is the product obtained by condensing only three components, namely, (a) a phenol from the. group consisting of phenol and meta ereiol, (b) formaldehyde, and (c) 'a watersoluble inorganic sulflte, said phenol and said formaldehyde being condensed below 0.,

1.5 mols of said formaldehyde and in the presence of an alkaline catalyst, to form a waterorganic suliite in the ratio of one mol of said sulfite to 3 to 8- mols of said methylol phenol, thereby to form methylene sulfonate groups in the resulting condensate, heating the sulfonated condensateof said three components in aqueous soluble methylol phenol, said methylol phenol then being reacted with said water-soluble inorganic sulflte in the ratio 'of one mol of said sulflte to 3 to 8 mols of said methylol phenol, thereby to form sulfonate groups in the resulting condensate, and, thereafter heating the sulfonated condensate of said three components in aqueous solution until the viscosity of a 50% aqueous solution thereof becomes, at least G on the Gardner-Holdt scale. WENDELL S. NIEDERHAUSER MATTHEW W. Mum-m. 

